Day 12: The Earth and a billiard ball

You might have heard about this urban legend: The Earth is actually smoother(*) than a billiard ball.

Sunrise over Cappadocia, Turkey. View from a hot air balloon ride.

Is it true? Yeah, quite. A standard billiard ball (American-style pool) must be 2.25″ in diameter (57.15 mm) and has a tolerance of 0.005 inches (0.127 mm). That’s pretty smooth: the ratio of the size of an allowable bump to the diameter is ~0.002.